GIH5-Gestion de Stock

8/8/2019 GIH5-Gestion de Stock

1/39

Chapitre 5

Gestion de stocks


2/39

- 2 -

Plan

Introduction

Fonctionnement dune pharmacie hospitalire

Inventory control subject to known demand

Inventory control subject to unknown demand

Retours la gestion de stocks pharmaceutique


3/39

- 3 -

Chane logistique pharmaceutique

Fournisseurs externes

Laboratoires

Distributeurs

Pharmacie centrale

Achat - Approvisionnement

Livraison

Pharmacie hpital

Rapprovisionnement

Production de certains mdicamentslivraison

Units de soins

Rception, stockage, administration et demandes urgentes

Rduction de cots

Scurisation ducircuit demdicament

(bon mdicament,au bon patient, aubon moment)

Pb de prissabilit


4/39

- 4 -

Chane logistique pharmaceutique

Fournisseurmdicaments

Fournisseurmdicaments

Fournisseurinstruments

Pharmacentrale

Pharma

hpital

Pharmahpital

Pharmahpital

Unitsoins

Unit

soins

Unitsoins

patients

HCL songe rduire le nombre de niveaux en livrant directement lesunits de soins partir de la pharmacie centrale.


5/39

- 5 -

Plan

Introduction






6/39


7/39

- 7 -


Gestion de stocks des units de soins:

Systmes darmoires (appro au service)

Systmes de chariots (appro la pharma)

Systmes de double bacs (plein/vide)Stocks de rserve pour besoins urgents

Forte pression pour la dispensation nominative


8/39

- 8 -


Ressource du secteur pharmaceutique:

Ressources humaines

Pharmaciens

Internes

Prparateurs

Agent de transport, de logistique

Locaux de stockage

Camions

Acteurs aval: infirmires des units de soins, mdecins


9/39

- 9 -


Point de vue des flux physiques:

Mdicaments des grandes consommations (chariots)

Mdicaments nominaux-chariots

Mdicaments nominaux avec ordonnances

Mdicaments avec fabricationPatients externes

Soluts

Armoires/stocks de pharmacie des services internes/externes

chariots des mdicaments durgence dans les services

Mdicaments rfrigrs (?)

Flux amont (fournisseur stockage)


10/39

- 10 -


Point de vue dinformations-dcisions:

Planning des activits : quand, par qui, comment

Rapprovisionnement des units de soins : quand, par qui, en fonction dequoi

mission et rception des commandes internes

Approvisionnements fournisseurs : quand, combien, par qui, en fonctionde quoi

Rception de commandes fournisseurs

Gestion des stocks et de transport


11/39

- 11 -


Les grandes tapes du circuit de mdicament

prescription validation dispensation administration


12/39

- 12 -


Flux global des mdicaments

Magasin

Soluts Fabrication PatientsMdicaments

nominauxMdicaments

de grande

consommation

Livraisons


13/39

- 13 -


Mdicament de grande consommation en chariots

based on

planning


14/39

- 14 -


Mdicament nominaux en chariots


15/39

- 15 -


Dispensation au guichet


16/39


17/39

- 17 -

Introduction

Investment in inventory is enormous

In the 3rd quarter of 1991, US invests $1.03 trillion, about 20-25% of GNP

Use of scientific inventory control methods leads to a significantcompetitive advantage.

Only replenishment of independent products is considered.Dependent demands are controlled byMRP.

Fundamental problem of inventory management:

When should an order be placed?

How much should be ordered? Major models: deterministic demand or stochastic one.


18/39

- 18 -

Types ofInventories

Raw material

Components subassemblies : items not yet reached completion Work in process (WIP, encours) : inventory waiting for processing or

being processed.

Finished goods

Spare parts for maintenance, replacement

Stock in transit


19/39

- 19 -

Motivation for holding inventories

Economy of scale (setup)

Uncertainties (demand, process, supply) Speculation

Transportation : in transit or pipeline inventories

Capacity smoothing : change in demand

Logistics: ensuring continuityy in purchasing, prod, distri,

Control costs


20/39

- 20 -

Characteristics of inventory systems

Demand: constant/variable, known/stochastic

Leadtime Review time: continuous review, periodic review

Excess demand: back ordered or lost

Changing inventory: perishability or obsolescence


21/39

- 21 -

Relevant costs

Holding cost (carrying cost, inventory cost) : proportion to the

amount of inventory physically on hand at any time.Includes:

physical storage cost,

taxes & insurance,

opportunity cost of alternative investment (most important.Usually,

Unit holding cost per year = annual interest rate . Value of one item unit

h = I . c


22/39

- 22 -

Relevant costs

(Fixed) Order cost : Usually,

where K is a fixed order handling cost, c is the unit purchase cost

0, 0( )

, 0.

if xC x

K cx if x

!!

"

Penality cost: shortage cost or stock-out cost. Interpretationdepends on whether the excess demand is backordered or lost.


23/39

- 23 -

The Economic Order Quantity (EOQ) model

Simplest and most fundamental model

Trade-off between fixed order cost & holding costsBasis for more complex system

Assumptions:

Demand rate know & constant D units/time unit

Shortage are not allowed

No order lead time

Cost include: fixed order cost K, unit purchase cost c, holding cost h


24/39

- 24 -


Q

T time

Inventory on

hand

2 2

2

cos 2

KD KDQ

h Ic

KThD

Total t KhD Dc

! !

!

!

Formule de Wilson

Remark: Q does not depend on c (why).


25/39

- 25 -


L time

Inventory onhand

R

Inclusion of order leadtime

By reorder point R = DL

Issue an order of Q units whenever the reorder point is reached.


26/39


27/39

- 27 -


Sensitivity (Case c = 0)

Optimal cycle time T* = (2K/Dh)0.5

(Power of 2) Choose T in ..., , , 1, 2, 4, ... such that T < T*


28/39

- 28 -

Quantity discount models

All-units discout

Example:

K = 8, D = 600, I = 0,2

C(Q)= .3Q, if Q < 500

= .29Q if 500


29/39

- 29 -

Plan

Introduction






30/39

- 30 -

Introduction

Management of uncertainty plays an important role in the success of

a firm Source of uncertainty: consumer preferences, trends in the market,

availability & cost of labor & resources, supply times, ...

Past observation can be used to estimate the probability distributionof the demand.

D = Ddet + Drand

Deterministic inventory models are appropriate:

When the variance of Drand is small w.r.t. Ddet

When the predictable variable is more important then the randomvariation

When the problem structure is too complexe to include an explicitrepresentation of randomness.

Often, randomness is too important to ignore it.


31/39

- 31 -

The Newsboy model (stock rotation nulle)

Single period single product model

Useful for highly fashion items, food, news papers.

Model:

Decision variable Q = number of units to be purchased at the

beginning of the period Demand d of the period is a random variable with density f(x) and

probability distribution F(x).

All relevant costs can be determined on the basis of the ending

inventory Q D Co = cost per unit of positive inventory (overage cost)

Cu = cost per unit of unsatisfied demand (underage cost)


32/39

- 32 -

The Newsboy model (stock rotation nulle)

Cost function:

Total costG(Q, D) = Co max(0, Q-D) + Cu max(0, D-Q)

Average cost

G(Q) = E[G(Q, D)]

Optimal policy

F(Q*) = Cu/(Co+Cu) : critical ratio

The model can be easility extended to discrete demand and toinclude starting inventory.

F(Q*-1) < Cu/(Co+Cu) < F(Q*)


33/39

- 33 -

Reorder point order quantity policy (r, Q)

Derive from the form of optimal solution of EOQ model

(r, Q) system: place an order of Q units when the inventory positionreaches r.

Assumptions:

Continuous review Demand is random and stationary with d units per time unit

Fixed supply lead time L

Type 1 service :

probability of not stocking out in the supply lead time >= E


34/39

- 34 -

Reorder point order quantity policy (r, Q)

Role of the demande during lead time L

DL = demand during LWith

DL = Ld

Where d is the mean demand in each elementary period and Wd the

standard deviation.

LD dLW W!

r

L

DL


35/39

- 35 -

Reorder point order quantity policy (r, Q)Type 1 service model

How much to order : Q = EOQ

When to order : Issue an order of Q when the inventory positionreaches the reorder point r.

Determine r such that

Prob{DL > r} = 1 E

FDL(r) = E

In practice, DL is approximated by a normal distribution. Then,

R = d.L + SSWhere SS is the safety stock with

SS = zE.WDL

And zE is the safety factor with *(zE) = E.


36/39

- 36 -

ABC Inventory Classification:Where To Focus Management Attention

GOAL: Determine the small # of items that account for the majority

of the cost (exploiting 80/20 rule) - which need a tighter inventorycontrol

Items classified as A, B, orC items based on thepercentage of annualsales that they command

A items: very tight control, complete records, regular review

B items: less tightly controlled, good records, regular review

C items: simple controls, minimal records, large inventories, periodic

review

Typical split between classifications: No more than 20% of the itemsas Class A; no less than 50% of the items as Class C.


37/39

- 37 -

ATypicalABC Curve

% of SKU

% of Total Dollar Value

A

B

C

20% 50% 100%

60%

90%

100%


38/39

- 38 -

Example: ABC Inventory Classification

SKU

F-1

F-3

F-7

H-1

H-3

H-4

H-6

J-1

J-3

K-3

Ann. Sales(units)

40,000

195,000

30,000

100,000

3,000

50,000

10,000

30,000

150,000

6,000

UnitCost

0.06

0.10

0.09

0.05

0.15

0.06

0.07

0.12

0.05

0.09

AnnualSales ($)

2,400

19,500

2,700

5,000

450

3,000

700

3,600

7,500

540

$45,390

Rank

7

1

6

3

10

5

8

4

2

9

Sales%

5.3

43.0

6.0

11.0

1.0

6.6

1.5

7.9

16.5

1.2

ABCClass


39/39

- 39 -

Plan

Introduction

Fonctionnement dune pharmacie hospitalire Inventory control subject to known demand



Documents

GIH5-Gestion de Stock